Sail

Abstract

An aerofoil sail, with two sailcloth sides of substantially equal area and shape, and an airspace between them, and includes vents by which the airspace may be inflated by the wind, and structure by which either side of the sail may be made shorter from tack to clew than the other.

I claim: 
     
       1. A sail including: at least two opposed flexible sheets,   at least one vent by which air may in normal use flow into a space between said flexible sheets, and,   at least one outlet vent by which air may in normal use flow out of said space between said flexible sheets, said sail taking in normal use an aerofoil shape having two outer faces comprised of said at least two opposed flexible sheets with a first said face having a greater useful surface area than the second said face, wherein said opposed flexible sheets are connected by at least one flexible element joined to both, forming at least one baffle, said at least one baffle extending substantially vertically between said opposed flexible sheets, and having at least one vent therein through which air may flow in normal use.   
     
     
       2. A sail as claimed in claim 1, including means by which said useful surface are of at least one said face of the sail can be adjusted such that said useful surface area of said at least one face of the sail can be made greater than that of the other. 
     
     
       3. A sail as claimed in claim 2, wherein said means includes apparatus by which non-adjacent parts of at least one said flexible sheet can be brought together, such that intervening parts of said at least one flexible sheet form a pocket which does not in normal use comprise apart of said useful surface area of either said face of the sail, and by which non-adjacent parts of said at least one flexible sheet can be disassociated, such that a pocket of intervening parts of said at least one flexible sheet is unformed. 
     
     
       4. A sail as claimed in claim 3, wherein said apparatus by which non-adjacent parts of said at least one flexible sheet or sheets can be brought together and disassociated includes lines integral with said non-adjacent parts. 
     
     
       5. A sail as claimed in claim 3, wherein said apparatus by which non-adjacent parts of said at least one flexible sheet can be brought together and disassociated includes at least one zip fastener having two engageable tracks, each of said engageable tracks being associated with a different one of said non-adjacent parts. 
     
     
       6. A sail as claimed in claim 3, wherein said at least one inlet vent is formed in said intevening parts of said at least one flexible sheet. 
     
     
       7. A sail as claimed in claim 1, wherein said at least two flexible sheets include central flexible sheet and two outer flexible sheets, wherein said central flexible sheet and a first said outer flexible sheet act in combination to provide a second side of said sail, said first said outer flexible sheet having a greater useful surface area than the other said outer flexible sheet.